To the accompaniment of finger-drumming and audible sighs from the rest of us on the flight, the late-arriving couple - who appeared to be 40-ish and, on first impression, normal - cheerily stuffed their belongings into the overhead bins and arrayed themselves on either side of the aisle in front of me. I say 'on first impression', because once we reached cruising altitude the man would lean across the divide every few minutes and poke his index finger into the woman's ear.

A captive audience to this bizarre ritual, I sat there, puzzlement fast giving way to disbelief. Any second now, I figured, she would rip her tray table from its moorings and bash her mate's face in. But she never did, even as he kept this up, sporadically, for two hours (and even as many of us wrestled with the urge to tear out our own tray tables and bash his face in). If anything, she seemed charmed by his behaviour. In fact, the way she swooned into his arms as we disembarked at JFK, you'd assume he'd been showering her with kisses all afternoon. I could only shake my head and dismiss them as Two Idiots Who Clearly Deserve Each Other.

Until later, that is, when the insight hit: what took place on that flight was a victimless crime; two consenting adults engaged in an eccentric but nonetheless mutually satisfying form of affection. Or maybe even - and God help us all here - foreplay. Contrast their quirky rapport with what I witnessed the very next evening at a trendy cafe in lower Manhattan. There I was, surrounded by young lovers - not that you'd know it from their behaviour. One twosome in particular caught my eye. The entire time they awaited their salads, she sat hunched over her chequebook while he leafed through a copy of Rolling Stone. Not so much as a cough passed between them. Meanwhile, off in the corner, the exceptional pair who were openly cooing at each other drew disapproving stares from just about everyone else. I was reminded of when, as a teenager, I'd be in the park making out with my girlfriend, and some mum and dad would stroll by with their kids, turn up their noses and murmur about how shameful we were. Except that, in this case, the disapproving murmurers themselves were barely out of their teens...

Something has happened to us. As couples, collectively, we are neither as playful nor as outwardly spontaneous as we once were. What's more, many of us will go to great lengths to justify that (d)evolution. After all, we're more level-headed, sophisticated and worldly-wise. We're millennial men and women! We've outgrown such silliness.

And what have we achieved with all of this worldly wisdom? The destruction of what we used to call - without the sarcastic smirk - 'romantic love'. It's not hard to understand how this happened. For one thing, we have a contemporary youth culture steeped in the previous generation's appalling level of romantic dysfunction. Nowadays I teach a college course in the personal essay, and my first assignment each semester is to have students produce a written 'inventory', if you will, of the important emotional milestones in their lives to date. Their work makes it clear to me that the average student has seen his or her parents go through divorce and remarriage and quite possibly divorce again, with an extracurricular dalliance or two thrown in for good measure. It's no shock that such kids should come of age believing that love is a many-splintered thing; that even 'true love' is transient. And so, loath to play the fool in their own romantic lives, they hold back something of themselves in anticipation of that inevitable rainy day. After all, nothing ventured, nothing lost.

Meanwhile, we seem to work overtime to discourage passion and spontaneity wherever we may find it. Here in the US, at least, we look with disfavour (if not actual legal suspicion) upon over-the-top displays of ardour. A latter-day Cyrano who stood beneath his beloved's window spouting intimate verse would fall foul of stalker laws in many jurisdictions. We suppress those flirtatious urges that strike us at the water cooler, lest somebody misconstrue and start screaming 'Harassment!', thereby costing us our jobs and reputations. Nor can one discount the impact of the self-help industry's vast relationships wing, with its tendency to distil all of humankind down to an immutable set of gender-specific traits - I'm from Mars, you're from Venus - and all those so-called advice books such as The Rules, which, by rigidly defining 'acceptable' mating rituals, make cookie-cutter pairings all but inevitable.

Indeed, how could these factors not conspire to take all of the magic and mystery out of courtship!

I recently encountered an old flame who spoke of her impending nuptials with all the starry-eyed sentimentality of a business analyst assessing the economy's inflationary potential. And an editor I know took his wife to a cosy restaurant for their anniversary, where they were subjected for the next hour to a young duo who swapped stock-fund appraisals, hi-tech titbits... everything but sweet nothings. Before long Mrs Editor leaned over to her husband and whispered, 'You know what? I feel like I'm back at the office!'

One hates to point fingers here, but women, especially, seem to be abandoning their timeless romantic idylls in favour of a far more utilitarian approach to the mating dance. Need proof? Check the tenor of personal ads run by the fairer sex. Increasingly, women spend less time effusing amorous whimsy than setting the height of a common-sense hurdle guys must clear in order to establish their fitness for serious relationships. 'Professional' is a word you see a lot in such ads. 'Financial security' also, apparently, sets today's women swooning. Not long ago I saw an ad from a woman who lusted for a suitor with 'clean credit'. This is not to imply that women should seek unstable bankrupts; lord knows they'll stumble across enough of those anyway. But clean credit?

Love comes in unusual packages. For all we know, Mr Ear Poker's odd habit was just a solitary manifestation of a lovable zaniness that enriches his relationship as a whole. Today's shop-manual approach to dating precludes that glorious alchemy between one singular man and one singular woman that promotes an enduring, highly individualised coupleness. We end up trawling for a 'unique' soulmate in a sea of clones. For my part, if it ever comes to choosing between an ear-poker and a woman who spends dinner lost in her chequebook, all I can say is, baby, I'm all ears...